Propane deaspihalting process



1965 A. K. REDCAY 3,262,605

PROPANE DEASPHALTING PROCES 5 Filed June 6, 1962 2 Sheets-Sheet 1 LIGHT OIL. SECONDARY VAPOFUZER- OIL STRJPPER g;

LIGHT EXTRACT L TO STORAGE AARON K REDCAV F n BYMWW ATTORNEY Aug. 24, 1965 A. K. REDCAY PROPANE DEASPHALTING PROCESS Filed June 6, 1962 2 Sheets-Sheet 2 HEAVY on. sacowwm VAFQRlZER.

S PE P ER i09 STRIPPER 42 -88 ASPHALT T0 STORAGE //6 l2! HEAVY RACT P To s-r xes M9 HEATER. I04 I A A A A N [06 -./.30 32 V! \V/ \V/ 1 \\/I I27 I30 H2O SEPARATOR fi- 85L r 62 k I JAsPHALT K FLASH 2 DRUM A34 m5) 1& INTERMEDIATE 7&7; PROPANE SURGE DRUM 431 M l /9 HIGH PRESSURE r PROPANE SURGE DRUM l 1 ,J

AARON K. REDCAY ATTORNEY INVENTOR United States Patent This invention routes to an extraction solvent recovery sytem and more particularly to a solvent extraction and recovery system operated in the region of the critical ten perature and pressure conditions of the extraction solvent with important advantages of economy in heat, equipment, extraction efficiency and recovery of solvent.

The invention is based upon the principle that operating in the region of critical temperature and pressure conditions of a readily volatile extraction solvent, only small changes of pressure coupled with heat exchange sufilce to change the volatile solvent phase from a gas to a liqui and vice versa, at relatively constant temperature. Another important result of such operation is that a liquefied normally gaseous solvent like propane becomes more selective the critical region.

In a further aspect of this invention, liquified propane gas is used as an extraction-deasphalting solvent for high boiling oils at relatively high temperature and pressure, still in the region of its critical conditions, wherein high boiling oils have their normal foaming tendency, particularly in viscous oils, greatly reduced by operation at cornparatively high temperatures.

In a specific aspect of this invention, gaseous solvent such as propane, and a liquid solvent solution and liquid propane are brought into heat exchange contact in the critical temperature and pressure areas whereby the propane gas at high pressure becomes liquified, and the liquid propane solvent at reduced pressure becomes vaporized for its separation from the light oil solution. The heat exchange contact is with simultaneous pressure variation upon the solution, and thus the liquifying gas gives up its heat of vaporization and the simultaneous vaporizing gas in the solution absorbs that heat of vaporization in the exchange. There results an approximately simultaneous change of phase, a condensation and evaporation in separate systems, both in the critical region, so that no substantial temperature change is necessary. However, preferred operation is at such high temperature that no foaming can take place.

The practical effect of such heat exchange contact allows recovery of the propane from the extract solution by a change of phase to a vapor, and simultaneous recovery of gaseous propane in a distinct system as liquid by its liquifaction in the heat exchange. The consequence is that the liquid propane becomes available from the gaseous propane and propane in solution becomes gasified, an important heat economy. It will be apparent that while the invention is most useful in conjunction with a propane deasphalting system, it is usefully used with other systems.

In a deasphalting system using liquid propane as solvent, distinct fractions treated under distinct vaporizing conditions are produced. That is, a fraction of relatively pure propane as against a propane solution in light oil or propane solution in heavy oil are separately produced, each having distinct vaporizing conditions. To produce these distinct fractions, the initial oil is either extracted twice in series; that is, fresh solvent is introduced into the first rathnate fraction, or the oil to be extracted initially is split into two distinct portions. The first extract fraction has the propane vaporized therefrom under comparatively high temperature vaporizing conditions to form a source of hot propane vapors under high pressure. The second fraction available by addition of liquid propane to either fiz the second of a series of extractions or by addition of liquid propane to a second portion of the split charge before vaporization of the propane, a solution of either light or heavy oil in propane, is reduced in pressure and then contacted by heat exchange with the propane vapors formed in the first vaporization of the propane extract. The temperature and pressure conditions remain close to the critical; for instance, between 103 to 200 F. and a pressure between 200 and 300 for the solution and, for the Vapor, between 460 and 500 p.s.i.g., whereby the propane vapors become liquified and the dissolved propane is vaporized from its solution in the heat exchange contact. The entire operation is effected at high enough temperature to avoid or reduce foaming of the oil by the vapors of propane as the propane therein is evaporated, with or Without additional heat supplied for this purpose.

The invention is further explained in reference to the drawings which show diagrammatically a propane deasphalting system operating with the principle of this intion. FIG. H is merely a direct extension of FIG. I, both the figures together illustrating the composite system.

It will be noted that the several extractions illustrated in the drawings are merely for purposes of demonstrating the principle of operation of a few stages and several other stages, as needed to effect a more complex separation, can be introduced as additional stages. Other solvents of approximate similar characteristics can be substituted and, particularly, other oil extraction stocks from various sources, petroleum, coal, gas tars, shale, including crude oils, partially refined, and residual oils, can be substituted for those herein described. Thus, an oil to be extracted is maintained in a storage supply tank It It may be of the character of any residual cut of a fractionating tower. It may be a heavy crude oil or any crude lube oil fraction of paraffin, naphthenic or asphaltic base, or partially refined oil such as a lube oil bright stock. The oil to be extracted is preliminarily heated in tank 10, as desired, to maintain it purnpably fluid by steam coils l5 and pumped by pump 11 by way of line 13 into line 12 at a temperature controlled in exchanger 17 as a tempering heat control to a desired extraction temperature; for instance, 160 to 200 F. It passes through line 12 and into the top of a primary separator 18, the system pressure for liquid propane being 400 to 500 p.s.i.g.

SERIES OPERATION For series operation, valve 14 is closed so that all of the oil from tank it to be extracted flows into line 12. Liquid propane in line lid is warmed by heat exchanger 21 to about the same temperature and enters the bottom of the contactor 153 at the temperature and the system pressure of 400 to 500 p.s.i.g. In the contactor 18 there are rotating discs indicated diagrammatically at 23, a construction conventional in the art for causing good extractive contact between the propane and the oil to be extracted. The temperature in the extractor can be further adjusted by a heating loop 25 mounted near the top, and through which steam can be circulated. For example, an ultimate temperature of to F. for a light oil soltuion is a useful control temperature in the contactor 18.

In the contactor 3189 an interface between extract and raffinate solutions is maintained by a level controller 27 which constricts a valve in line 22 through which raffinate solution is withdrawn. A relatively light oil-propane solution passes overhead through line Zll, mixes with hot recycle oil in line 42, and the mixture passes by line 41 to a dash drum as in which propane gas separates and leaves overhead through line 44.

A portion of the light oil extract solution still containing about 3 to 50% of propane comprising the flash drum 31 in line 29. to a temperature of about 150 to 185 F overhead extract solution I tron and propane as a second extract'and passes into line bottoms'of drum 36 is Withdrawn by way of lines 43 and 45 at a rate controlled by a liquid level controller which constricts valve 47 passing to a secondary propane vaporizer 49A and is heatedto about 320, to350 F.,' for further separation of most of the residualpropane from the extract solution. V

Another portion of .the flash drum bottoms withdrawn through line 43 is passed by pump 39 to heater 38 by way of line 40. Light oil supplied to heater 38 is heatedtherein, s-ufiicient to provide the necessary heat for several propane vaporizing steps. It leaves the heater through line 42 and a first portion is mixed with the light oil propane solution in line and thence by line 41 to drum 36 to separate the main portion of propane gas. A second portion passed through line 63 is separated and used for other heating purposes. [For instance, a portion is taken-01f through line 69 for heating the secondary propane vapor- V izer 49A. Thereafter, the heating oil leaves through line 67, is passed into the drum 36 for its lower temperature heat, is withdrawn through45 as flashdr-um bottoms and returned to vaporizer 49A for removal of propane and passes thence as light oil with only a small 1 to 5% content of propane for further treatment through line 70.

- Another portion of the heating oil in line 63is'withdrawn through line 6 1 for further heating of heavy oil separator recycle at exchanger 58, the partially spent heater oil being returned to the dash drum 36 by way .of lines 65 and 67. Other heat applications of the heater oil in line 6-3 are effected through line 43 as will appear.

The hot propane gas flashed overhead from flashclrum .36 in line 44 is now use-d in heat exchange, at the pressure of the system, about 400 to 500 p.-s.-i.g., and at the slightly raised vaporizing temperature of about 180 to 185 F. in a manner as will appear. 7

The separated heavy oil-propanesolutionrfrom cont-actor 1 8 is withdrawn through line 22 at a rate controlled by the liquid level controller 27 and is passedinto line 26, valve 24 being open and valve 16 being closed. The heavy oil and propane solution in line 25 passes into a second contactor2-8 where it is again extracted with a fresh, supply of high normal systems pressure liquid propane from line 19. The heavyoil and propane solution from the first separator bottom is preferably at a temperature of 110 to 120 CR, and the propane from line 19 at a'pressure of 400 to 500 p.s.i.g. is preheated by heat exchanger preferably about 180 tional heat being supplied through steam coil 33; The temperature is usually adjusted to be about the same as the propane vapors overhead of the flash drum 44. The

comprises the heavier oil fraccontrolled by a level controller 35 through line 32 and,

F., close temperaturecontrol addisent to heater 104 (FIG, II) for propane recovery, as 7 will appear.

Thus, in the initial operation as series extraction, there provided a hot gaseous recovered propane fraction in l ne s44 at a temperatureof about 180 to 185.F. and a liquid extract solution of a heavy oil and propane which passes overhead in line 30 at the same pressure of 400 to 5 Q0 p.s.i.g. and approximatelythe same temperature of 180 to185F. V V r The propane gas through line 44 passes through heat exchanger-46 under close'to critical conditions of 120 to 185 Band 400 to 500 p.s.i.g., and simultaneously the liquid extract solution in propane atabout the same temperature passes by line 30 through heat exchanger 46in heat exchange contacttherewith. However, just' prior to entering the heat exchanger 46, the pressure on line 30 is reduced .to the range of 200m 300 p .s.i';g.; for example,

about 225m 250 p.s.i;g. atthepressure reducing valve 43.

Consequently, the propane in solution after passing the valve 48 tends to evaporate at the' reduced pressure and, in doing so, will absorb heat from the propane vapors passing through the heat exchanger 46 from line 44. In the exchange, the pro-pane vapors in line 46 Wlll tend to become cooler and liquify, transferring its heat of vaporization to the propane in solution. The net effect is that the propane in solution leaving the heat exchanger 46 through line 52 tends to be converted to vapors and the 'vap orous propane in line 44 tends to be condensed to a liquid as it leaves the exchanger through line 60.

The essential diiferences in the systems is merely the pressure difterence. However, to further raise the-temperature somewhat more for more efficient vaporization .of the propane in the solution leaving the exchanger 46 and particularly 'in order to prevent foaming of the vaporizing gas leaving the viscous oil, .a recycle line 55 taking oil bottoms from the evaporator 5'4- leads to exchanger 58 for further heating by a'heating oil coil fed by line 61, which, as mentioned, takes hot oil from line 63 and returns it to line 65 after transfer of heat in exchanger 58 to the recycle oil in line 55. The now heated recycle oil in line 55 is mixed with the partially vaporized mixture of oil and propane in line 52 after leaving exchanger 46 and the hotter mixture of both pass by way of line 56 into the evaporator 54 for separation of propane vapors.

The pro-pane vapors separated in evaporator 54 pass overhead through line 62 at a pressure of,.for example, be

feed from line 6 3 as mentioned above, returning the par tially spent heating oil by line 65 to the'fiash drum 36. Most of the residual propane which may be present in the heavy oil bottomsin line 57 from about 3 to 50% of the heavy oil extract, is vaporized and passes overhead through line 86 joining the propane vapors in line 62 for ultimaterecovery as dry propane vapors. Line 62 also takes the dry propane vapors of line 70, evaporated from separator 49A. The dry heated light extract oil containing only a few percent, up to about 5% of propane, is withdrawn from evaporator 49A through line 72 and sent to higher temperature separator, 74 into which steam at about 600 F; is passed through line 716. The steam and. i residual propane vapors pass overhead into line 78. Simila-rly, the dry heated heavy oil extract in secondary evaporator 49Bcontaining its same small quantity of residual propane is withdrawn through line 88 andheated in high.

steam entering through linetemperature separator 93 with 92 and the steam and propane ,vapors pass overhead through line 94 into line 78.

The solution in line 30,'it will be noted,.is of liquid propanein the heavy oil extract phase and'it leaves the separator 28 as overhead, the raffinate leaving the separator 28 through'line 32. That raflinate also containing substantial quantities of propane is sent to a heater 104 and heated to about 500 F., passing thence by line'ltio to an asphalt flash drum 108' from which propane vapors at a pressure of about 225 to 250 ,p.s.i.g. pass overhead through line 110 into line62'for recovery as dry propane vapors. The hot heavy, oil extract bottoms from flash drum 1'68 pass to an asphalt stripper 112 by way of line 109, the last propane vapors being striPPed therefrom by.

live steam at about 600 propane and steam line 78. i

F. entering through-line llLithe passing overhead through line l! into 'Residual and extracted light and heavy oils from which a drawn through line 116 and sent by pump 118 through line 121 to asphalt storage.

The hot mixture of propane gas and steam in line 78 overhead of strippers 74, 0 and W3, are condensed by condenser 122 converting the steam to Water, which is separated in knockout drum 124, the water being dithdrawn through line 125, and the overhead propane gas in line 127 is picked up by compressor 128 and sent by line 13b to join the dry propane in line 62, both passing to line 134, cooled to about llt) to 180 F. and sent to low pressure propane surge drum 132. Any residual Waters collected are withdrawn through line 133. The propane withdrawn through line 136 is compressed to the system pressure of 400 to 560 p.s.i.g. by one or more of several pumps 138, and recycled to the system through line 1%, or sent to a liquified propane surge and storage drum 14%? by Way of line 19A from which compensating supplies may be withdrawn from time to time for feed to the system by Way of line 135. The Warm condensed propane in line 66 still at the system pressure following heat exchange through exchanger 56, is returned to the high pressure surge drum 139, through line till for feedback into the system.

It will be noted in operation of this system that a first separation taking place in separator 18 divides the oil into separate solutions of a light oil and heavy oil fraction, both of which contain dissolved propane. The relative light and heavy oil components in each fraction are variable with the temperature, pressure and quantity of solvent, which is highly selective in the critical range of 400 to 500 psig. and 110 to 185 F. Consequently, when the railinate bottoms solution from the separator 18 is sent to the second separator 28 mixed by additional liquid propane, two separate solutions are formed and a further selective separation is performed, the residual oil raflinate from separator 18 separating into tWo fractions again variable with exact temperature and pressure conditions which, however, can remain constant or be varied by heat from steam coil '25 in separator 18 and from steam coil 33 in separator 28. Since the pressure and temperature conditions are restricted to be close to the critical, no Wide variation in temperature and pressure is needed While maintaining the propane in the liquid extraction phase. Nevertheless, close separation into several fractions, two separations as shown, or several more fractions as may be further useful, are possible because of the high selectivity of the solvent in the critical area. For securing the advantages of heat exchange as described, any vaporized solvent at the high pressure of the system and at a high temperature still near the critical may be passed in heat exchange with any extract solution of the liquified solvent available from any of several extraction stages, reducing the pressure upon the solution whereby with heat exchange the actual heat of vaporization and condensation is respectively exchanged at approximately the same temperature, the gaseous solvent being condensed to liquid for ready reuse in the system and the gas in solution being evaporated for recovery of extracted liquid.

Inasmuch, however, as the evaporating gas from a viscous oil tends to cause foaming, it is useful to effect sepa ration of the gas from the oil at a comparatively high temperature, still under the critical conditions. Thus, the separation Will desirably be at a temperature of about 170 to 190 F. for propane and a reduced vaporizing pressure of 200 to 300 p.s.i.g., preferably 225 to 250 p.s.i.g. Thus, the system as described is flexible to product any of several select fractions, to effect asphalt removal from oil with propane as is known; to effect important heat economies by vaporization, condensation, exchange of latent heats; and to eiiect gas and oil separation under non-foaming conditions.

SPLIT FLOW OPERATION As described above for series operation, the oil is extracted, recovering propane vapors at high pressure from the light oil extract fraction and the ralfinate solution con taining some dissolved propane is reextracted by addition of more propane forming a comparatively heavy oil extract solution in propane. It is the propane vapors of the first extraction that are passed in heat exchange with the relatively heavy oil second extract solution containing additional propane which is passed in heat exchange to efiect vapor condensation and solvent separation in the exchange, it, of course, makes no ditierence for the heat exchange operation from What particular sources either the propane vapors or the propane solutions are obtained, provided that they are under close to critical temperature and pressure conditions When they are passed in heat exchange.

In an alternate split flow method of operating, the main charge is first split into two streams. The first stream is extracted With propane to produce an extract and ratfinate and propane gas is recovered from the extract fraction, the total rafiinate being sent directly to heavy oil or asphalt recovery. The second of the split streams is independently extracted and the extract fraction comprising light or heavy oil and propane and Without separating the propane therefrom is passed in heat exchange with the propane gas Which was recovered from the first stream extract, thus to reduce the propane vapors to a liquid by the heat exchange With the second split stream liquid extract solution, the dissolved propane in the solution being simultaneously vaporized. The modified split stream procedure is as follows:

With valve 14 open, a hot feed in line 12. is split, a half of the charge passing directly into separator 13 and separating an overhead fraction as before in line 2d, comprising propane and light oil from which the propane is recovered from flash drum by way of line as overhead. The high pressure liquid phase, the asphalt-propane residue, is Withdrawn from separator 1% through line 22 passing by line 32, valve 16 being open and valve 2% being closed, to asphalt recovery in furnace 184. The second half of the split charge in line 12, With valve 14 open, passes by Way of line 34 into line 26, and thence to separator 28 Where it is contacted with fresh liquid propane from line 19. The liquid propane passing to the separator .23 by Way of line 27 may be heated by a heat exchanger 31 to a temperature of to F. The overhead light oil and propane may have been further heated by coil 33 to a temperature as high as F, and pass through line 35), and have its pressure reduced as it passes through heat exchanger 44?, adjusted by reducing valve 58, and tends to flash vapors of propane. The propane solution in line 52 after pressure reduction and heat transfer is mixed with hot heat exchanger 53, oil being Withdrawn from the bottom of separator by Way of line 55. That hot oil is further heated in an exchanger 58 to a temperature of 200 to 250 F. by a hot oil leg 61 passing exchange oil therethrough from heater line 63, returning the hot oil to line d5. Thus, the reheated separate cycle split extract oil in line 55 admixes with the vapors and oil in line 52 for supply of additional heat, thereby tending to completely vaporize the propane therein as it is returned to the separator 54. by way of line 56.

The split stream, it will be noted, operates just like the series stream in the subsequent stages. The procedures differ only in that the solution for heat exchange contact at &6 to be contacted with propane vapors from line 44 differs. For series fiow that solution is the second extract solution obtained by extracting the rai'finate of the first extraction. For split stream the original oil is divided into two fractions. The first extract has its propane removed as vapors for subsequent heat exchange liquifaction in both procedures. In the series flow the liquid solution for that heat exchange is the second extract performed on the first extraction raflinate. In the split stream i'low the liquid solution is the extract solution of a portion or the original feedstock split for this purpose.

The following is a specific example of the operation of this invention: 7

' Example I An asphaltic crude is toppedto550 F., and the cold, heavy oil from storage is preheated to 150 F. and pum'ped for admixture with anequal volume of liquid propane to an agitating separator at a pressure of 470 p.s.i.g., the propane being at the same temperature. Both pass countercurrently through the separator, while heating the upper portion to a temperature of about 150 F. An interface forms in the separator and is maintained below the middle of the separator by Withdrawal of extract overhead and rafiiniate bottoms from below, continuously from the separator. The extract is preheated to 185 F. by mixture with hot recycle heating oils obtained as bottoms from a Y flash drum, and the mixed recycle bottoms and extract solution from the separator are returned to the flash drum and the vaporized propane is removed as overhead as gaseous propane at the flashtemperature of 185 F. and at about the pressure of the system, 470 p.s.i.g. The raf-. finate fraction from the separator is sent to a secondseparator to which another equal volume of liquid propane at a temperature of 150 F. and a pressure of 470 p.s.i.g. is passed countercurrently and simultaneously toform two more fractions, an interface again forming and being maintained below the middle of the separatorby an'extract fraction taken overhead and a rafiinate fraction withdrawn from the bottom of the separator, continuously. The liquid extract fraction of the second separator is preheated to about 175 F. and sent to a heat exchanger through which the propane vapor, the'same overhead vapor from the flash drum evaporation of the first separatorextract fraction, is passed simultaneously. The conditions of the propane-vapors passing through the heat exchanger is maintained as obtained from the flash drum; that is, a temperature of 185 F. and a pressure of 470 p.s.i.g. The 175 F. extract solution from the second separator, however, has its pressure reduced to 235.p.s.i.g continuously as it enters the heat exchanger. During the heat exchange,

' propane gas becomes liquifiedas high pressure liquid propane at the system pressure of 470 p.s.i.g and at a temperature of about 175 F. The second extractor liquid solution at reduced pressure of 235 p.s.i.g. after passing through the heatfexchanger is immediately contacted and admixed with an equal volume of bottoms cycle solution obtained from an evaporator, the solution before mixture having been heated to a temperature of 225 F. and the mixed bottom cycle solution and the reduced pressure solution following heat exchange being both sentto. the

same evaporatorso that low pressure propane. vapors at.

235' p.s.i.g. pass overhead ofthe evaporator, and a bottoms solution containing about.30% propane and the.

heavy oil separator extract fraction is withdrawn from the evaporator, reheated in'a heat exchanger to 225 F, and

recycled to the inlet for admixture with the heat exchange contacted second separator extract solution. The propane separates in the evaporator at this temperature from the heavy oil extract solution without significant foaming. There is thus obtained (a) independent extract fractions of the original oil by the plurality of extractions formed extract oil without substantial foaming; and ((1) several extractfractions of the initial oil are producable by slight stream for heat exchange propane vaporization against the propane vapors at high pressure. obtained from heating the extract ofthe first stream slightly above its critical tern perature. V

' While the system has been described with respect to a propane deasphalting system, the principles hereof may be applied to other solvents for selective extraction of other. organic liquids. Various modifications in such systems will occur to those skilled in the. art. 'Accordingly, it is intended thatthe description be regarded as illustrative and not limiting except as defined in the claims appended hereto. Y i

I claim: i

1. The method of operating a' solvent extraction system comprising contacting an extractable oil with a liquified volatile solvent at a temperature and pressure close to the critical at which the liquid solvent is converted to a gas and separating the extract phrase from the railinate phase, heating the extract phase sufiicient to flash the solvent into vapors at the pressure of'the system, extracting the raflinate with fresh solvent under condiitions similar'to; the first extraction to produce a second extract phase, and-then passing the extract phase of the second extraction into heat exchange with the solvent vapors at the high temperature and pressure as recovered by adding additional liquid propane to the rafiinate-propane solution obtained from a preceding extraction to convert it into separate solutions; (b) the propane vapors sary for vaporizing propane from'the second extract'fraction is obtained in the heat exchange; and, (c) by further.

heating at least the partially vaporized extract solution with heated recycle oil from the evaporator, a large portion of the propane becomes vaporized and from heavy system.

vapors from said heat exchange are recycled for further extraction in the system. I

3. The method of claim l'wherein the vaporized solvent in said heat exchange is separated from saidextract,;and then rcc ompr essed, condensed and ultimately recycled for, further use as an extraction agent in said 7 The method of claim 1 wherein the solvent solution mixture ,with solvent vaporsvaporizedfrom the solution in the heat exchange is further heated and passed'to an evaporator to separate additional solvent vapors whereby reduced foaming takes place in the evaporator at the raised temperature. 7 7 5. The method of claim 1 wherein the solvent solution mixture with solvent vapors vaporized from the solution in the heat exchange is further heated by mixing with a heated bottoms stream taken from an evaporator, and the mixed vapors, solventsolution and heated bottoms are'passed to the said evaporator for separation wherein reduced foaming takes place in said evaporator at the raised temperature. a l 6. The method as defined in claim 1 wherein the solvent is propane and the organic liquid is petroleum oil.

7; The method as defined inclaim 6 wherein the petroleum oil contains asphalt's which are separatedwih the raflinate produced with the extract solution. 7

oil as solutions of the liquid propane, heatingtheextract solution sufiicient to flashbtl most of the propane as vapors at the said pressure of the system, withdraw aaoaeos ing the raffinate solution and admixing it with additional liquid propane whereby to form additional separable layers of extract and rafiinate solutions in the same temperature and pressure ranges, passing the second extract solution at a reduced pressure in the range of 200 to 300 p.s.i.g. in heat exchange contact with the propane vapors at the said system pressure obtained from heating the first extract solution whereby to liquify the vapors of said propane at the system pressure and substantially vaporize propane from their said second extract solution, further heating the vaporous mixture following the heat exchange and passing the same to an evaporator to separate pro pane vapors overhead.

9. The method as defined in claim 8 wherein the vaporized propane from the heat exchange is recompressed and cooled to high pressure liquid propane, admixed with the liquified propane obtained in said heat exchange and recycled to the extraction system.

10. The method as defined in claim 1 wherein the extract fraction of the oil passed in heat exchange to vaporize dissolved propane therein is obtained by an extraction performed upon a separate stream of the original oil feed.

11. The method of operating a solvent extraction system comprising separating an extractable oil into separate first and second portions, contacting both portions with a liquified volatile solvent at a temperature and pressure close to the critical at which the liquified solvent is converted to a gas, separating the extract phase from the raffinate phase of each separately extracted portion, heating the extract phase of the first extracted portion sufilcient to vaporize the solvent at the pressure of the system and passing the heated vapors thereof into heat exchange contact with the separated second extract phase While slightly reducing the pressure on the said second extract phase whereby the solvent therein is substantially vaporized to a gas and the said heated vapors are simultaneously liquified.

12. The method as defined in claim l1 wherein the partially vaporized extract fraction of the second stream, following heat exchange, is further heated for separation of vapors from extract oil at substantially raised temperature with reduced foaming.

References Cited by the Examiner UNITED STATES PATENTS 2,079,886 5/37 Voorhees 208-309 2,500,757 3/ 50 Kiersted 208--309 2,616,912 11/52 Dickinson 208309 2,650,897 9/53 Woerner 20845 2,850,43 1 9/58 Smith 208-309 DELBERT E. GANTZ, Primary Examiner.

ALPHDNSO D. SULLIVAN, Examiner. 

1. THE METHOD OF OPERATING A SOLVENT EXTRACTION SYSTEM COMPRISING CONTACTING AN EXTRACTABLE OIL WITH A LIQUIFIED VOLATILE SOLVENT AT A TEMPATURE AND PRESSURE CLOSE TO THE CRITICAL AT WHICH THE LIQUID SOLVENT IS CONVERTED TO A GAS AND SEPARATING THE EXTRACT PHRASE FROM THE RAFFINATE PHASE, HEATING THE EXTRACT PHRASE SUFFICIENT TO FLASH THE SOLVENT INTO VAPORS AT THE PRESSURE OF THE SYSTEM, EXTRACTING THE RAFFINATE WITH FRESH SOLVENT UNDER CONDITIONS SIMILAR TO THE FIRST EXTRACTION TO PRODUCE A SECOND EXTRACT PHASE, AND THEN PASSING THE EXTRACT PHASE OF THE SECOND EXTRACTION INTO HEAT EXCHANGE WITH THE SOLVENT VAPORS AT THE HIGH TEMPERATURE AND PRESSURE AS RECOVERED FROM THE FIRST EXTRACT WHILE SLIGHTLY REDUCING THE PRESSURE OF THE SECOND SOLVENT EXTRACT PHASE WHERE, BY THE HEAT EXCHANGE AND SLIGHT REDUCTION OF PRESSURE ON TH EXTRACT PHASE, THE SOLVENT DISSOLVED IN SAID EXTRACT PHASE IS CONVERTED TO VAPORS AND THE VAPORIZED SOLVENT SEPARATED FROM THE FIRST EXTRACT IS LIQUIFIED. 